Light scattering techniques typically utilize a flow cell constructed from an optically transmitting material such as glass. The flow cell is configured to enable passage of a liquid sample through a bore formed in the solid material of the flow cell. A laser beam is directed through the solid material into the bore where it irradiates the liquid sample residing therein. In response to this irradiation, light rays propagate from the bore through the solid material at various angles. One or more light detectors situated external to the flow cell receive the light rays and typically convert the optical signal into an electrical or digital signal, which is thereafter processed and conditioned by electronics as needed to derive information regarding the analytes contained in the irradiated liquid sample.
Two commonly utilized light detectors are a static light detector and a dynamic light detector. The static light detector operates on the principle of light scattering intensity measurement (or static scattering, or Rayleigh scattering). The light intensity scattered by a molecule in solution that is small compared with the wavelength of the incident laser beam is proportional to the concentration multiplied by the molecular weight. Thus, for example, if the concentration of the molecules in solution is known or is measured during the analysis process, the molecular weight averages and distributions can be determined. The dynamic light detector operates on the principle of dynamic light scattering measurement (or quasi-elastic light scattering, or photon correlation spectroscopy). In dynamic light scattering detection, the translational diffusion coefficient of the molecules moving randomly in the solution is calculated from the autocorrelation function of the scattered light. These very small signal values may be collected by utilizing a solid state photon counter such as an avalanche photodiode and autocorrelator electronics incorporating high-speed digital signal processors. From the diffusion constant, the hydrodynamic radius can be calculated by utilizing the Stokes-Einstein equation.
An ongoing need exists for improvements in the design of flow cells utilized in light scattering processes. Such improvements include, for example, miniaturization so that the flow cell may be successfully utilized in a wide range of analytical systems such as various types of chromatography systems, as well as enhanced performance (e.g., signal-to-noise ratio, data resolution, instrument sensitivity, etc.). In addition, the flow cell and its corresponding components should be designed so as to be flexible and versatile to meet the needs of a wide variety of light scattering processes.